imperative

When something absolutely has to be done and cannot be put off, use the adjective imperative.

Imperative is from Latin imperare "to command," and its original use was for a verb form expressing a command: "Do it!" is an imperative sentence. It's still used that way, but it's more commonly applied to something so pressing it cannot be put off: "Hiring new workers has become imperative." It has more immediate force than pressing but less than urgent.